1. Field of the Invention
The present invention is generally related to sun detection sensor systems, and particularly to sun detection sensors that protect critical components of infrared cameras and other thermal imaging devices from accidental exposure from direct sunlight. The critical components include Sensors made of materials including amorphous silicon or vanadium oxide, which are ordinarily used in uncooled Infrared Cameras.
2. Description of the Related Art
Thermal imaging devices such as infrared cameras are used for detecting and imaging objects which emit an infrared signal generated by their hot body or exhaust signature. For example, they can be employed to detect fires, overheating machinery, airplanes, vehicles and people and to control temperature sensitive industrial processes. Thermal imaging devices operate by detecting the differences in thermal radiance of various objects in a scene and by displaying the differences as a visual image of the scene. Thermal imaging devices include optics for collecting and focusing thermal radiation from a scene, a thermal detector having several thermal sensors for converting thermal radiation to an electrical signal and electronics for amplifying and processing the electrical signal into a visual display.
Infrared cameras are utilized during a wide range of environmental conditions, ranging from night time through bright sunny days. The sun as a black body produces intense radiation throughout the entire infrared band. Infrared cameras have great difficulty detecting targets, when the sun rays are directly in the field of view. The amount of solar radiation can be extremely large when compared to the radiation signals from the objects to be detected. In these instances, solar radiation is capable of saturating the infrared detector and damaging it. Additionally, solar radiation can reduce the sensitivity in a viewed scene thus producing a blurred image of the scene.
Infrared cameras can be broadly divided into two types: those with cooled infrared image detectors and those with uncooled infrared image detectors. Uncooled infrared cameras, use a detector which operates at an ambient temperature. Cooled infrared image detectors require bulky, expensive cryogenic coolers to operate.
Uncooled infrared cameras do not require cryogenic coolers because they do not need to be cooled to low temperatures. They are equipped with small temperature control elements which maintain the detector at about ambient temperature. All modern uncooled infrared cameras use detectors that work by the change in resistance, voltage, or current when heated by infrared radiation. These changes are measured and compared to the values of the operating temperature of the detector. The detectors of the uncooled infrared cameras can be stabilized at an ambient operating temperature to reduce image noise. Uncooled infrared cameras detectors comprise pyroelectric and ferroelectric materials that are designed based on microbolometer technology. These detectors are known as infrared microbolometer sensors, which are suited to operate at ambient temperatures.
Infrared detectors are generally made of vanadium oxide and amorphous silicon and are used as sensors in uncooled infrared cameras and other equipments which are likely to be damaged by exposure to direct sunlight.
It is known in the art to protect infrared detectors from potentially damaging exposure to direct sunlight. Optical filters can be used to eliminate or reduce saturation, blooming and/or damage to the equipment and imaging by the exposure to the sunlight. Many such filters are, however, inadequate in providing protection and may result in black or blurred scene image. Other electronic techniques are deficient because they can be affected by the large flux produced by radiation from the sunlight. It is therefore desirable to provide an apparatus and method for limiting the damage to infrared detectors caused by direct exposure to the sunlight. Accordingly, it is an object of our present invention to provide an apparatus and method to protect infrared cameras and other thermal imaging devices from the undesirable and damaging effects of exposure to direct sunlight.
It is another object of our invention to locate the sun detection sensor separately as a universal attachment to an XT infrared camera and away from the optic lens, to protect optic lens from the effects of undesired radiation.
It is further object of our invention to provide a simple and inexpensive attachment which is removably attached to the infrared camera. The attachment will be used only when there is possibility of getting undesired radiation.